The United States is the only developed country that does not offer paid leave to new parents on a national level. But four states now offer paid leave, and the study focused on two of the first to do so. California and New Jersey each introduced six weeks of partially paid leave to new parents in 2004 and 2009, respectively.

California pays up to 55 percent of a parent's salary, while New Jersey covers 67 percent of a parent's salary.

University of California, San Francisco researchers analyzed data from the two states and found that paid family leave helped increase breastfeeding rates, but the rates increased most among higher-income women who could afford to take more time off from work.

"Our findings suggest that women in states that enacted paid family leave modestly extended breastfeeding during infancy, which is a critical developmental window," said study first author Dr. Rita Hamad. She's an assistant professor of family and community medicine at UCSF.

"It's notable that we see the breastfeeding changes particularly among women of higher social status, a group that is presumably more likely to take advantage of the partially paid leave," Hamad said in a university news release.

"These policies only provide new parents with a fraction of their regular salary, so low-income parents may be less likely to take time off," she said.

"Providing fully paid leave might give low-income mothers and fathers the support to be with their newborns," Hamad added.

Two other states have introduced paid family leave, including Rhode Island (2014) and New York (2018).

The study was published Oct. 25 in the American Journal of Public Health.

More information

The U.S. Office on Women's Health offers a guide to breastfeeding (https://www.womenshealth.gov/files/documents/your-guide-to-breastfeeding.pdf ).

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.